Gas compression system and method utilizing gas seal control

ABSTRACT

A gas compression system and method according to which product gas is introduced into and compressed in, a compressor. A portion of the compressed gas is discharged to external equipment, and a portion of the gas is trapped in response to deactivation of the compressor. The trapped gas is passed back to the deactivated compressor.

BACKGROUND

[0001] This invention relates to a gas seal control system and methodfor a gas compressor, and, more particularly, to such a system andmethod according to which a seal gas is applied to a gas seal in thecompressor.

[0002] Gas compressors are well known, and include a housing forreceiving a product gas to be compressed, a shaft rotatably mounted inthe housing, and an impeller fixed to the shaft and cooperating withstationary vanes for compressing the gas before the compressed gas isdischarged from the housing.

[0003] In many of these arrangements, one or more gas seals are oftenprovided around the shaft between the impeller and the respective endsof the shaft for minimizing leakage of the gas from the high pressurearea. During operation of the compressor, at least a portion of theproduct gas from the compressor is introduced to the seals to maintain ahigh pressure sealing effect. However this product gas often containsforeign matter, such as dirt, iron filings, and other solid particleswhich can contaminate the seals. Therefore, a seal gas from an externalsource is sometimes introduced to the seals to prevent possiblecontamination of the seals. However, the external seal gas, which isusually nitrogen, is relatively expensive and must be stored andtransported from the external source to the compressor, which furtheradds to the cost.

[0004] Therefore, what is needed is gas compressor in which relativeclean seal gas can be applied to the seals without significantly addingto the cost.

SUMMARY

[0005] According to the system and method of an embodiment of thepresent invention, a product gas is introduced into and compressed in, acompressor. A portion of the compressed gas is discharged to externalequipment, and a portion of the gas is trapped in response todeactivation of the compressor. The trapped gas is passed back to thedeactivated compressor and functions as a seal gas.

[0006] This embodiment enjoys the advantages of utilizing product gas asa seal gas to eliminate the costs associated with a separate seal gas.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007]FIG. 1 is a schematic view of a gas compression system accordingto an embodiment of the present invention.

[0008]FIG. 2 is a schematic view of a gas compression system accordingto an alternate embodiment of the present invention.

DETAILED DESCRIPTION

[0009] Referring to FIG. 1 of the drawings, the reference numeral 10refers, in general, to a gas compression system according to anembodiment of the present invention. The system 10 includes a gascompressor 12 which can be of a convention design and, as such, includesa shaft 14 rotatably mounted in a housing 16. Although not shown in thedrawing for the convenience of presentation, it is understood that animpeller is fixed to the shaft 14 and cooperates with stationary vanesfor compressing the gas when the compressor 12 is activated in aconventional manner.

[0010] A seal 18 is provided on the shaft 14 and extends between theimpeller and the upstream end of the shaft. The seal 18 is also of aconventional design and, as such, is adapted to seal against the leakageof the high pressure gas developed by the compressor during itsoperation and is adapted to receive a high pressure gas in a manner tobe described to promote its sealing action. A typical seal of this typeincludes a rotating member that mounted on the shaft 14 for rotationwith the shaft, and a fixed member positioned in very close proximity tothe rotating member. One of the seal members, usually the rotatingmember, has minute indentations or pockets machined in its outer face sothat, when it rotates, pressure is created between it and thecorresponding face of the other member which separates the two faces.This creates a very small through area through which gas can flow.Examples of these type of seals, or similar seals, are disclosed in U.S.Pat. Nos. 5,441,283; 5,492,341; 5,498,007; 5,700.013; and 5,713,576 thedisclosures of all of which are incorporated by reference.

[0011] The compressor 12 is connected in a closed loop conduit, shown ingeneral, by the reference numeral 20, extending from the outlet of thecompressor and back to its inlet for recycling at least a portion of thecompressed gas under conditions to be described. A conduit 22 isconnected to the conduit 20 for introducing product gas from an internalsource, and at a predetermined pressure, in the direction indicated bythe flow arrow under the control of a block valve 24 connected in theconduit 22. The gas then flows through a portion of the conduit 22 to acooler 26 for the cooling the gas, in a conventional manner.

[0012] The relatively cool gas from the cooler 26 is introduced into aninlet of the compressor 12 which operates in a conventional manner tocompress the gas to a pressure higher than the inlet pressure utilizingthe impeller and vanes discussed above. The compressed gas dischargesfrom the compressor 12 through an outlet and passes back into theconduit 20 downstream of the compressor.

[0013] A discharge conduit 30 is connected to the conduit 20 downstreamof the compressor 12 for receiving at least a portion of the compressedgas. The conduit 30 discharges the compressed gas to external equipment(not shown) under the control of a valve 32 connected in the conduit. Arecycle control valve 36 is connected in the conduit 20 downstream ofthe conduit 30 for reasons to be described.

[0014] A conduit 40 is connected to the conduit 20 just downstream ofthe outlet of the compressor 12 and extends parallel to a section of thelatter conduit. The conduit 40 is connected back to the conduit 20upstream of the conduit 30. Two spaced block valves 42 and 44 areconnected in the conduit 40 and are normally open to permit the flow ofsome of the compressed gas from the outlet of the compressor 12 into theconduit 40 through which it flows parallel to the flow of the remaininggas through the latter portion of the conduit 20. The block valves 42and 44 are normally open but can be closed to capture some of the gas inthat portion of the conduit 40 extending between them, under conditionsto be described.

[0015] One end of a conduit 50 is connected to a section of the conduit40 extending between the block valves 42 and 44. The conduit 50 extendsthrough an inlet of the compressor 12 and to the seal 18. A normallyopen control valve 52 is connected in the conduit 50 for controlling theflow of gas through the conduit. A filter 54 is also connected in theconduct 50 for filtering foreign matter, such as dirt, iron filings,liquid, etc. from the gas as it passes through the latter conduit underconditions to be described.

[0016] In the initial, normal operation of the system 10, the valves 24,32, 42, 44, and 52 are opened and the valve 36 is closed. Product gas,at a predetermined inlet pressure, is introduced into the conduit 22 forpassage to the conduit 20, through the cooler 30, and into thecompressor 12. The compressor 12 is activated by turning on its motorswitch, or the like, to compress the gas to a pressure above the inletpressure, and the compressed gas exits the compressor outlet and passesback into, and flows through, the conduit 20. Since the valves 42 and 44are open, some of this gas passes from the conduit 20 into the conduit40 through which it flows parallel to the flow of the remaining gasthrough the corresponding, parallel portion of the conduit 20. A portionof this gas passes from the conduit 40, into and through the conduit 50,and through the filter 54 under the control of the valve 52. The gas iscleaned in the filter 54 in the manner discussed above, exits the filter54 and passes through the open control valve 52 and to the seal 18 inthe compressor 12. This clean gas functions to prevent pressure loss andto keep the dirty process gas out of the area between the faces of theseal 18 to minimize contamination of the seal.

[0017] The remaining portion of the gas in the conduit 40 isreintroduced into the conduit 20 and thus mixes with the gas flowingthrough the latter portion of the conduit. This mixed gas then passesfrom the conduit 20, into the conduit 30, and passes 2 through the openvalve 32 to external equipment for further processing or use.

[0018] There are certain conditions when it is desired to recycle atleast some of the compressed gas from the compressor 12. For example,design requirements may require that the gas discharged from the conduit30 must be at a relatively low flow, in terms of cubic feet per minute,for example, which flow is lower than the lowest flow that is possiblefrom the compressor 12. In this case, the valves 42, 44, and 52 are opento permit gas flow through the conduits 40 and 50 as discussed above.The valve 36 is opened and the valve 32 is set at a position to outputgas from the conduit 20 at the relatively low flow. Thus, the portion ofthe gas outputted by the compressor 12 in the conduit 20 that does notflow into the conduit 30 is recycled back through the conduit 20, theopen valve 36, and to the cooler 26 for passage back to the compressor12. The remaining gas needed to meet the minimum output flow of thecompressor 12 is supplied from the incoming process gas through theconduit 22, as discussed above. This recycle loop can also be usedduring start up and shut down of the system 10.

[0019] When the compressor 12 is deactivated by the tripping off of itsmotor, either on purpose to shut down the system, or due to anelectrical or system failure, or the like, the valves 24, 32, 42 and 44are closed and the valve 36 is opened. This can be done automatically ina conventional manner in response to the tripping off of the motor. Theclosing of the valves 24 and 32 isolates the system 10 from the flow ofthe process gas into, and the discharge of the gas from, the conduit 20and the inlet and discharge gas pressure from the compressor are thusthe same. The opening of the valve 36 allows any gas remaining in thesystem to recycle back through the remaining portion of the conduit 20to the compressor 12.

[0020] According to a feature of the invention, the closing of thevalves 42 and 44 in response to the tripping of the compressor motordiscussed above traps the gas in that section of the conduit 40extending between the latter valves. This trapped gas is at the samepressure and temperature as the gas discharging from the compressor 12,and the open valve 52 allows the latter gas to flow, at a pressure thatis above the inlet pressure of the compressor 12, through the filter 54.Foreign matter is removed from the gas in the filter 54 and the cleangas then passes to the gas seal 18 in the compressor 12 to prevent thedirty process gas from contaminating the gas seal and prevents anypressure loss, as discussed above.

[0021] The system 10 thus enables relatively clean process gas to beintroduced to the gas seal 18 in the compressor 12 after shut down ofthe compressor without incurring the expense of providing clean gas froman external source.

[0022] Referring to the alternate embodiment depicted in FIG. 2 of thedrawings, the reference numeral 60 refers, in general, to a gascompression system according to another embodiment of the presentinvention. The system 60 includes a gas compressor 62 which can be of aconvention design and, as such, includes a shaft 64 rotatably mounted ina housing 66. Although not shown in the drawing for the convenience ofpresentation, it is understood that an impeller is fixed to the shaft 64and cooperates with stationary vanes for compressing the gas when thecompressor 62 is activated in a conventional manner.

[0023] A seal 68 is provided on the shaft 64 and extends between theimpeller and the upstream end of the shaft. Since the seal 68 isidentical to the seal 18 of the previous embodiment, it will not bedescribed in any further detail.

[0024] The compressor 62 is connected in a closed loop conduit, shown ingeneral, by the reference numeral 70, extending from the outlet of thecompressor and back to its inlet for recycling at least a portion of thecompressed gas under conditions to be described. A conduit 72 isconnected to the conduit 70 for introducing product gas from an internalsource and at a predetermined pressure in the direction indicated by theflow arrow under the control of a block valve 74 connected in theconduit 72. The gas then flows through a portion of the conduit 72 to acooler 76 for the cooling the gas, in a conventional manner.

[0025] The relatively cool gas from the cooler 76 is introduced into aninlet of the compressor 62 which operates in a conventional manner tocompress the gas to a pressure higher than the inlet pressure utilizingthe impeller and vanes discussed above. The compressed gas dischargesfrom the compressor 62 through an outlet and passes back into theconduit 70 downstream of the compressor.

[0026] A discharge conduit 80 is connected to the conduit 70 downstreamof the compressor 62 for receiving at least a portion of the compressedgas, under conditions to be described, and discharging the compressedgas to external equipment (not shown). A pair of spaced block valves 82and 84 are provided in the conduit 80 for controlling the flow of thegas through the conduit. The block valves 82 and 84 can be closed tocapture some of the gas in that portion of the conduit 80 extendingbetween the block valves 82 and 84, as will be described.

[0027] A recycle control valve 86 is connected in the conduit 70downstream of the conduit 80 for controlling the flow of gas through thelatter conduit under conditions to be described.

[0028] One end of a conduit 90 is connected to the conduit 70 at a pointjust upstream of the connection of the conduit 80 to the conduit 70. Theconduit 90 extends from the conduit 70, through an inlet of thecompressor 62, and to the seal 68. A pair of spaced valves 92 and 94 areprovided in the conduit 90 for controlling the flow of gas through thelatter conduit, and a filter 94 is also connected in the conduct 90between the latter valves for filtering foreign matter, such as dirt,iron filings, liquid, etc. from the gas as it passes through the conduit90.

[0029] A conduit 100 extends from the conduit 80 between the valves 82and 84 to the conduit 90 just downstream of the valve 92. A block valve102 is connected in the conduit 90 for controlling the flow of gas fromthe conduit 80 to the conduit 90 under conditions to be described.

[0030] In the initial, normal operation of the system 60, the valves 86and 102 are closed and the valves 72, 82, 84 92, and 94 are opened.Product gas, at a predetermined inlet pressure, is introduced into theconduit 72 for passage to the conduit 70, through the cooler 80, andinto the compressor 62. The compressor 62 is activated by turning on itsmotor switch, or the like, to compress the gas to a pressure above theinlet pressure, and the compressed gas exits the compressor outlet andpasses back into, and flows through, the conduit 70.

[0031] Since the valves 82, 84, 92 and 94 are open, some of thecompressed gas from the compressor 62 passes from the conduit 70, intothe conduit 80, and passes through the open valves 82 and 84 anddischarges from the system 60 for passage to external equipment forfurther processing or use. Another portion of the compressed gas fromthe compressor 62 passes from the conduit 70, into the conduit 90, andinto and through the open valve 92 and the filter 96 under the controlof the valve 94. The filter 96 operates to clean the gas as discussedabove, and the relatively clean gas passes to the seal 68 in thecompressor 62. The relatively clean gas functions to prevent pressureloss and to keep the dirty process gas out of the area between the facesof the seal 68 and thus minimizes contamination of the seal.

[0032] If it is desired to recycle at least some of the compressed gasfrom the compressor 62, for the reasons set forth above in connectionwith the embodiment of FIG. 1, the valves 92 and 94 are opened to permitthe flow through the conduit 90 as described above. The valves 82 and 84are set at a position to output gas from the conduit 70 at a relativelylow flow rate and the valve 86 is opened. This permits the remainingportion of the gas in the conduit 70 downstream of the conduit 90 to berecycled back through the valve 86 to the cooler 76 for passage back tothe compressor 62. The remaining gas needed to meet the minimum outputflow of the compressor 62 is supplied from the incoming process gasthrough the conduit 72, as discussed above. This recycle loop can alsobe used during start up and shut down of the system 60.

[0033] When the compressor 12 is deactivated by the tripping off of itsmotor, either on purpose to shut down the system, or due to anelectrical or system failure, or the like, the valves 74, 82, 84 and 92are closed and the valves 86, 94, and 102 are opened. This can be doneautomatically in response to the tripping off of the motor in aconventional manner. The closing of the valves 74, 82 and 84 isolatesthe system 60 from the flow of the process gas into, and the dischargeof the gas from, the conduit 70 and the inlet and discharge gas pressurefrom the compressor are the same. The opening of the valve 86 allows anygas remaining in the system to recycle back through the remainingportion of the conduit 70 to the compressor 62.

[0034] According to a feature of the invention, when the valves 82 and84 close as a result of the shut off of the motor of the compressor 68as described above, some of the gas in that section of the conduit 80extending between the latter valves is trapped. This gas, which is atthe same temperature and elevated pressure as the gas discharging fromthe compressor 62, then flows through the open valve 102, into theconduit 90 downstream of the valve 92, and into the filter 96. Foreignmatter is removed from the gas by the filter 96 before the clean gasflows through the open valve 94 and to the gas seal 68 in the compressor62 to prevent pressure loss and possible contamination of the seal bythe process gas in the compressor, as discussed above.

[0035] Thus the embodiment of FIG. 2 enjoys all of the advantages of theembodiment of FIG. 1.

[0036] It is understood that variations may be made to each of the aboveembodiments without departing from the scope of the invention. Forexample, more than one gas seal be provided in the compressor and anyother type of device, other than a filter can be used to clean the gas.Further, although the flow lines were referenced as being in the form of“conduits” it is understood that any type of flow line can be used.

[0037] Since other modifications, changes, and substitutions areintended in the foregoing disclosure, it is appropriate that theappended claims be construed broadly and in a manner consistent with thescope of the invention.

What is claimed is:
 1. A gas compression system comprising a compressorfor receiving product gas and compressing the gas, a first conduit forreceiving compressed gas from the compressor, a second conduit forreceiving some of the compressed gas and trapping the latter gas whenthe compressor shuts down, a third conduit connecting the second conduitto the compressor for passing the trapped gas back to the compressor,and a cleaning device disposed in the third conduit for cleaning thetrapped gas before it is passed to the compressor.
 2. The system ofclaim 1 further comprising two spaced valves in the second conduit, thevalves being movable from an open position in which gas flows throughthe second conduit to the third conduit, and a closed position in whichgas is trapped in the second conduit between the valves.
 3. The systemof claim 2 wherein the valves are open during operation of thecompressor and closed when the compressor shuts down.
 4. The system ofclaim 3 wherein the trapped gas passes from the second conduit to thethird conduit for passage back to the compressor after the compressorshuts down.
 5. The system of claim 1 further comprising a gas sealdisposed in the compressor and wherein the clean gas passes from thethird conduit to the gas seal.
 6. The system of claim 1 wherein thesecond conduit receives some of the compressed gas from the firstconduit.
 7. The system of claim 1 further comprising a fourth conduitconnected to the first conduit for discharging the compressed gas in thefirst conduit from the system.
 8. The system of claim 7 wherein thefourth conduit discharges a portion of the compressed gas and whereinthe first conduit is connected to the inlet of the compressor forpassing another portion of the gas back to the compressor.
 9. The systemof claim 1 further comprising a fourth conduit connected to the secondconduit for discharging the compressed gas in the first conduit from thesystem.
 10. The system of claim 9 wherein the fourth conduit dischargesa portion of the compressed gas and wherein the first conduit isconnected to the inlet of the compressor for passing another portion ofthe gas back to the compressor.
 11. The system of claim 1 wherein thecompressor has an inlet for receiving the gas from an external source,and an outlet for discharging the compressed gas, the first conduitconnected to the inlet and the outlet of the compressor for receivingcompressed gas from the outlet, passing the gas in a loop, and returningthe gas back to the inlet.
 12. A gas compression system comprising acompressor having an inlet for receiving product gas and an outlet fordischarging the compressed gas; a first conduit connected to the inletfor receiving compressed gas; a second conduit connected to the firstconduit for discharging at least a portion of the gas from the system; athird conduit connected to the first conduit for receiving some of thecompressed gas and trapping the latter gas when the compressor shutsdown; a fourth conduit connecting the third conduit to the compressorfor passing the trapped gas back to the compressor when the compressorshuts down, and a cleaning device disposed in the fourth conduit forcleaning the trapped gas before it is passed to the compressor.
 13. Thesystem of claim 12 further comprising two spaced valves in the thirdconduit, the valves being movable from an open position in which gasflows through the third conduit back to the first conduit, and a closedposition in which gas is trapped in the third conduit between thevalves.
 14. The system of claim 13 wherein the valves are open duringoperation of the compressor and closed when the compressor shuts down.15. The system of claim 14 wherein the trapped gas passes from the thirdconduit to the fourth conduit for passage back to the compressor afterthe compressor shuts down.
 16. The system of claim 12 further comprisinga gas seal disposed in the compressor and wherein the clean gas passesfrom the fourth conduit to the gas seal.
 17. The system of claim 12wherein the first conduit is also connected to the inlet of thecompressor and passes a portion of the gas in a loop before returningthe gas back to the inlet.
 18. A gas compression system comprising acompressor having an inlet for receiving product gas and an outlet fordischarging the compressed gas; a first conduit connected to the inletfor receiving compressed gas; a second conduit connected to the firstconduit for discharging at least a portion of the gas from the system; athird conduit connected to the second conduit for receiving some of thecompressed gas and trapping the latter gas when the compressor shutsdown; a fourth conduit connecting the third conduit to the compressorfor passing the trapped gas back to the compressor when the compressorshuts down, and a cleaning device disposed in the fourth conduit forcleaning the trapped gas before it is passed to the compressor.
 19. Thesystem of claim 18 further comprising two spaced valves in the thirdconduit, the valves being movable from an open position in which gasflows through the third conduit back to the second conduit, and a closedposition in which gas is trapped in the third conduit between thevalves.
 20. The system of claim 19 wherein the valves are open duringoperation of the compressor and closed when the compressor shuts down.21. The system of claim 20 wherein the trapped gas passes from the thirdconduit to the second conduit for passage back to the compressor afterthe compressor shuts down.
 22. The system of claim 18 further comprisinga gas seal disposed in the compressor and wherein the clean gas passesfrom the fourth conduit to the gas seal.
 23. The system of claim 18wherein the first conduit is also connected to the inlet of thecompressor and passes a portion of the gas in a loop before returningthe gas back to the inlet.
 24. A gas compression method comprising thesteps introducing product gas into a compressor, activating thecompressor for compressing the gas in the compressor, receiving thecompressed gas and discharging a portion of the compressed gas toexternal equipment, trapping a portion of the compressed gas in responseto deactivation of the compressor, and passing the trapped gas back tothe deactivated compressor.
 25. The method of claim 24 wherein thetrapped gas is passed to a gas seal in the compressor to prevent productgas being compressed from entering the gas seal.
 26. The method of claim25 further comprising the step of cleaning the trapped gas before itpasses to the gas seal.
 27. The method of claim 24 wherein the step oftrapping comprising the steps of providing a conduit for receiving aportion of the compressed gas during operation of the compressor,connecting two spaced valves in the conduit and closing the valves whencompressed gas is in the conduit.
 28. The method of claim 27 wherein thevalves are normally open to permit compressed gas to flow through theconduit and wherein the valves are closed when the compressor isdeactivated to trap the gas.
 29. The method of claim 28 wherein the stepof passing comprising the steps of opening the valves to allow thetrapped gas to pass back to the deactivated compressor.
 30. The methodof claim 24 further comprising the step of recycling a portion of thecompressed gas back to the inlet of the compressor.